Counterbalance mechanisms including a pair of interconnected parallelograms linkages, which are provided with counterbalance springs, are well known, as disclosed in U.S. Pat. Nos. 2,131,693; 3,426,190; 4,447,031; and, 5,180,136, which patents are incorporated by reference in their entireties herein. Counterbalance mechanisms having individually adjustable counterbalance springs are also known in the art, as shown in U.S. Pat. No. 4,447,031. It is also known to provide a mechanism for controlling vertical movement of a surface, such as a desk, a table top or a shelf relative to a supporting base wherein a counterbalance mechanism is provided to balance at least part of the weight of the surface and/or weight supported thereon and a brake mechanism is provided to releasably retain the surface in a desired vertical position, as taught in U.S. Pat. Nos. 4,130,069; 4,360,180; 4,559,879; 4,747,353; 4,981,085; 5,181,620; and, 5,797,331, which patents are incorporated by reference in their entireties herein. Moreover, a counterbalance mechanism employing a pivotally supported member coupled via cables to a surface to be supported for vertical movement and a spring for controlling pivotal movement of the member are taught in U.S. Pat. Nos. 5,181,620 and 5,797,331.
Devices having heavy and/or large moveable covers or enclosures regularly require a means for controlling the movement of the cover. Such covers and enclosures often are repeatedly manipulated from one position to another, e.g., open and closed positions, or moved through a range of motion, e.g., 10-60 degrees. As this movement must be performed by a user of the device, such as a person and not a powered machine, assistance must be provided to the user in order to facilitate and control the movement. If the foregoing assistance is not provided, the cover or enclosure may be difficult if not impossible to move, or in the alternative, a situation may exist where the user can not control the movement of the cover thereby resulting in damage to the cover.
A tanning bed is an example of such a device. Production variations in these devices cause variability in the location of the center of gravity of the tanning bed lid. Moreover, the size and nature of the tanning bed lids may require that the lids be rotatably connected at each end so that the lid moves evenly.
As can be derived from the variety of devices and methods directed at providing counterbalancing forces for an enclosure cover, many means have been contemplated to accomplish the desired end, i.e., consistent, balanced and controlled forces to the cover. Heretofore, tradeoffs between expense, complexity and performance were required.